1. Field of the Invention
This invention relates generally to carbon and graphite composite articles and more particularly to high strength fiber reinforced carbon and graphite composite articles.
2. Description of the Prior Art
With the rapid advance of aircraft, nuclear and aerospace and high temperature technologies there is an ever increasing need for new types of high strength composition materials that are capable of reliably withstanding high temperatures and pressures. Additionally, new methods are required to expeditiously fabricate these materials into articles having a wide variety of complex and intricate shapes. Examples of such articles include thin wall leading edges, radiation shields, aircraft brakes, nozzle inserts and nose tips as well as various types of structures having thin wall webs.
Numerous types of carbon and graphite composite articles and the methods for producing such articles have been described in the prior art. Although many of these methods and products have significantly contributed to the support of the advancing technologies, they have not been entirely suitable in applications where final part densities and physical dimensions must be controlled to very close tolerances, and where high strength articles having superior friction and wear characteristics are required. Applicant is familiar with the following prior art disclosures which illustrate the inadequacy of the prior art for accurate control of product shape, cross-sectional configuration, density, fiber volume and internal fiber orientation.
______________________________________ PATENTEE PATENT NO. ISSUE DATE ______________________________________ Dosker 2,653,890 Sep. 29, 1953 Labino 2,658,848 Nov. 10, 1953 Rusch, Rumson 2,743,207 Apr. 24, 1956 Labino 3,053,715 Sep. 11, 1962 Gibson, et al. 3,174,895 Mar. 23, 1965 Bickerdike, et al. 3,233,014 Feb. 1, 1966 Bickerdike, et al. 3,238,054 Mar. 1, 1966 Hough 3,462,340 Aug. 19, 1969 Watts 3,367,812 Feb. 6, 1968 Bourdeau, et al. 3,369,920 Feb. 20, 1968 Wainer, et al. 3,374,102 Mar. 19, 1968 Beasley 3,407,038 Oct. 22, 1968 Rohl, et al. 3,462,289 Aug. 19, 1969 Olstowski, et al. 3,502,759 Mar. 24, 1970 Williams, et al. (Br.) 1,163,979 Mar. 7, 1967 ______________________________________
The only patents of those enumerated which are considered to be even remotely pertinent to the invention as disclosed herein are the U.S. Pat. to Bickerdike, Nos. 3,233,014 and 3,238,054, the U.S. Pat. to Bourdeau, et al. No. 3,369,920 and the British patent to Williams, et al. The only similarity between the inventions described in these patents and my invention, however, resides in the fact that similar furnace processing conditions can be used for coating carbon or graphite fibers with pyrolytic materials. The patents neither describe nor suggest the novel and important substrate optimization techniques described herein, and clearly cannot be combined to suggest to one skilled in the art, applicant's novel techniques for accurate control of product shape, cross-sectional configuration, density, fiber volume and internal fiber orientation.
The Bickerdike patents describe the formation of a substrate of organic wool or fabric which is first treated with a resin and then carbonized. After carbonization, the substrate is infiltrated with pyrolytic carbon by subjecting it to elevated temperatures in a benzene/nitrogen atmosphere.
The method of my invention as described and claimed herein is uniquely different from Bickerdike in that I do not use organic fibers in the form of wool or cloth prior to the infiltration step. Rather, I use either a graphite or carbon fiber which can be a high strength, high modulus fiber in the form of cloth, yarn, tow or three-dimensionally woven panels. Most importantly, my invention does not involve a carbonization step, and thereby avoids the problems of spontaneous substrate shrinkage and distortion which are inherent in the carbonization step. Also avoided is material property variation due to carbonization, such as low or high shrinkage areas due to variations in the precursor.
Because the carbonization step is not necessary in the method of my invention and due to the novel and unique way in which I optimize the substrate for final product application prior to infiltration, my invention permits the controlled fabrication of a wide range of intricate and complex high strength composite articles specifically tailored for given end product uses.
The British patent to Williams, et al. is specifically directed toward various furnace processing techniques for the gas of fibrous materials and for the densification of fibrous substrates through the controlled deposition of pyrolytic materials. While the final step of my process also involves substrate densification, it is important to note that an important feature of my process relates to the novel way in which the basic substrate is optimized for densification. Additionally, where Williams relies solely on furnace processing techniques to control final part densities, in my invention substrate optimization provides the basic means for final part density control with furnace processing techniques serving as a supplementary fine control over final article density.
3. Definition of Terms
a. Carbon fibers are fibers produced by the heat treating of both natural and synthetic fibers of materials such as, for example, wool, rayon, polyacrolynitrile and pitch at temperatures on the order of 1000.degree. C.
b. Graphite fibers are fibers produced by the heat treating of carbon fibers at graphitizing temperatures on the order of 2000.degree. C. or more.
c. Pyrolytic carbon, as the term is used herein, refers to the carbon material which is deposited on a substrate by the thermal pyrolysis of a carbon bearing vapor.
d. Pyrolytic graphite is a trade name which has been given to carbon deposited from a hydrocarbon as over the temperature range of 1750.degree. to 2250.degree. C. It is a specific high temperature form of pyrolytic carbon.
e. Pyrolytic carbon infiltration is a term used to describe the carbon densification processing of porous fibrous and particulate substrates.